To access the "Quick Update Translations" app in Lightning, follow these steps:
- Open Salesforce and locate the App Launcher icon (usually found in the upper-left corner of the screen).
- Click on the App Launcher icon to open the launcher, search for "Quick Update Translations" and click on it as shown in the image below -

- The app will open, allowing you to start using its features immediately.

P.S. Discover Quick Update Translations, the simple way to update Labels and Translations in just a few clicks. Find it on AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=fa9afbfe-74ff-4027-ac32-2cdfd58184d3